[Synchrodyne]

I also looked more closely at the Eddystone EC958/12 ISB circuitry. This was a single-box receiver, but the ISB section was largely separate in what was called the “top tray”. Here the reference 100 kHz carrier for sideband demodulation was generated locally and phase-locked to the recovered carrier, obtained via the usual very narrow filter. There was also a second “loop” that was essentially an AFC system that fed back to the incremental tuning oscillator in the main receiver section, thus “steering” the tuning system to keep the 100 kHz carrier centred in its narrow filter.

I don’t know whether there was any Marconi influence in the EC958/12 design. It was a derivative of the EC958/7, released in 1973, which was the improved version of the original EC958, including digital readout and enhanced stability. The original I think, although released after the Marconi buyout of Eddystone, was essentially a legacy-Eddystone product. The EC958/5 was the marine GP-SSB version of the original, also (or only) rebadged as the MIMCO Nebula. And the EC958/7 was rebadged as the Marconi W/T H2311. So Marconi might have been involved to some extent with the rework that produced the EC958/7.

Marconi had previously rebadged a variant of the Eddystone 880 as its H2301 specifically for SSB (but not ISB) work. Although how it sat relative to Marconi’s own HR120 single-box receiver is unknown. In a broad sense, the EC958 series was the successor to the 880, so the H2311 might have been seen as following on from the H2301. To some extent the 880 had been Eddystone’s offering in some of the same markets at which the Racal RA17 was aimed, but unlike the latter, it does not appear to have had a corresponding ISB adaptor developed for it.

Cheers,